How to convert a txt file to JSON file and transform the content to JSON

I will walk down the memory lane in this tutorial. I got to think about an assignment I got at one of my first employments back in the days. The assignment was to change a big text file with a lot of entries, into a JSON object. This was a typical assignment for a junior developer, since it would require a lot of copy-paste from one file to another. But I solved this by a simple function in NodeJs instead.

Problem statement

I will show three scenarios in this tutorial that we will use. The first one will be quite simple, we will change a text file that looks like this:

Richard
Peter
Lisa
Emelie
Stephen
Taylor
Nina

Into a JSON object that looks like this:

{
  "persons": ["Richard", "Peter", "Lisa", "Emelie", "Stephen", "Taylor", "Nina"]
}

Our second scenario will be a little bit harder. We will convert a text file that looks like this:

Richard,23
Peter,12
Lisa,54
Emelie,23
Stephen,11
Taylor,32
Nina,2

To an object like this

{
  "persons": [
    {
      "name": "Richard",
      "age": 23
    },
    {
      "name": "Peter",
      "age": 12
    },
    {
      "name": "Lisa",
      "age": 54
    },
    {
      "name": "Emelie",
      "age": 23
    },
    {
      "name": "Stephen",
      "age": 11
    },
    {
      "name": "Taylor",
      "age": 32
    },
    {
      "name": "Nina",
      "age": 2
    }
  ]
}

Our third scenario will transform a text file that looks like this:

cars:
tesla
volvo
ford
mercedes
motorcycles:
yamaha
suzuki
harley davidson

To a JSON object that looks like this:

{
  "cars": ["tesla", "volvo", "ford", "mercedes"],
  "motorcycles": ["yamaha", "suzuki", "harley davidson"]
}

Solution one

Create a file called converter.js. Now, let's solve this step by step.

• We will use "fs" in node for our file reading/writing

const fs = require("fs");
const data = fs.readFileSync("./persons.txt", "utf8");

• Change the data to an array of names

const persons = data.trim().split("\n");

• Create our JSON structure in a const

const json = {
  persons: [],
};

• Add each person to the array and write the new file

persons.forEach((person) => {
  json.persons.push(person);
});

fs.writeFileSync("./persons.json", JSON.stringify(json, null, 2));

That's it. This scenario was quite simple, but imagine doing this manually for 500 names...

Full solution looks like this

const fs = require("fs");

const data = fs.readFileSync("./persons.txt", "utf8");

const persons = data.trim().split("\n");
const json = {
  persons: [],
};

persons.forEach((person) => {
  json.persons.push(person);
});

fs.writeFileSync("./persons.json", JSON.stringify(json, null, 2));

Solution two

For our next solution, we will need to handle the ages as well for each line. The logic we will change is basically in the forEach loop.

persons.forEach((person) => {
  const parts = person.split(",");
  json.persons.push({
    name: parts[0],
    age: Number(parts[1]),
  });
});

So what we are doing here is basically splitting the string by the comma and creating an array of 2 places. So Peter,12 will be ["Peter", "12"]. And then we are creating our JSON object with the two parts, and creating a number from the string.

Full code

const fs = require("fs");

const data = fs.readFileSync("./persons.txt", "utf8");

const persons = data.trim().split("\n");
const json = {
  persons: [],
};

persons.forEach((person) => {
  const parts = person.split(",");
  json.persons.push({
    name: parts[0],
    age: Number(parts[1]),
  });
});

fs.writeFileSync("./persons.json", JSON.stringify(json, null, 2));

Solution three

All right, last solution now guys. First, we change the name of our file and the constants to reflect the problem a little bit better.

const fs = require("fs");

const data = fs.readFileSync("./vehicles.txt", "utf8");

const vehicles = data.trim().split("\n");

Change our json constant as well to only be an empty object.

const json = {};

And in our loop, we need to check for ":" in order to create the new object. We also need to keep track of the "key" of the object to know where to put our next vehicle.

let currentKey = "";
vehicles.forEach((vechicle) => {
  if (vechicle.endsWith(":")) {
    currentKey = vechicle.substring(0, vechicle.length - 1);
    json[currentKey] = [];
  } else {
    json[currentKey]?.push(vechicle);
  }
});

• currentKey will hold the current key (cars or motorcycles in this case)
• If the "vehicle" ends with :, then we know it is a new key so we create a new entry in our json object
• If it is not ending with :, we add it to the currentKey in the json object
• vechicle.substring(0, vechicle.length - 1) this line is so we only store cars for example and not : at the end

Full code

const fs = require("fs");

const data = fs.readFileSync("./vehicles.txt", "utf8");

const vehicles = data.trim().split("\n");
const json = {};

let currentKey = "";
vehicles.forEach((vechicle) => {
  if (vechicle.endsWith(":")) {
    currentKey = vechicle.substring(0, vechicle.length - 1);
    json[currentKey] = [];
  } else {
    json[currentKey]?.push(vechicle);
  }
});

fs.writeFileSync("./vehicles.json", JSON.stringify(json, null, 2));

Outro

All right, that's it for this tutorial. Today we learned how we can transform a text file to a json file in NodeJs and also how we can programmatically change the plain text to a json object of our choice. This type of scenarios are not that common, but when they do occur, it can be nice to know how to face them.

I hope you found this interesting, and if you have another use case that is harder than the ones I showed here, please reach out and we can see if we can solve it together. Contact info is found here.

All the best,